1. Field of the Invention
The present invention relates to an alternating current driven type plasma display device and a method for producing an alternating current driven type plasma display.
2. Description of the Related Art
As an image display device that can be substituted for a currently mainstream cathode ray tube (CRT), flat-screen (flat-panel) display devices are studied in various ways. Such flat-panel display devices include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display device (PDP). Of these, the plasma display device has advantages that it is relatively easy to form a larger screen and attain a wider viewing angle, that it has excellent durability against environmental factors such as temperatures, magnetism and vibrations, and that it has a long lifetime, and so on. The plasma display device is, therefore, expected to be applicable not only to a home-use wall-hung television set but also to a large-sized public information terminal.
In the plasma display device, a voltage is applied to discharge cells having discharge spaces charged with a discharge gas comprising a rare gas, and a fluorescence layer in each discharge cell is excited with a vacuum ultraviolet ray generated by glow discharge in the discharge gas, to thereby give light emission. That is, each discharge cell is driven according to a principle similar to that of a fluorescent lamp, and, generally, the discharge cells are put together on the order of hundreds of thousands to constitute a display screen. The plasma display device is largely classified either as a direct current driven type (DC type) or an alternating current driven type (AC type) according to methods of applying a voltage to the discharge cells. Each type has advantages and disadvantages. The alternating current driven type plasma display device (hereinafter, referred to also as “plasma display device”) is suitable for attaining a higher fineness, since separation walls which work to separate the individual discharge cells within a display screen can be formed, for example, in the form of stripes. Further, it has an advantage that electrodes for discharge are less worn out and have a long lifetime since surfaces of the electrodes are covered with a dielectric layer comprising a dielectric material.
As an example of the plasma display device, a so-called tri-electrode type plasma display device is described, for example, in each of JP-A Nos. 5-307935 and 9-160525.
FIG. 1 shows a schematic exploded perspective view of a portion of a typical tri-electrode type plasma display device. In the plasma display device, discharge takes place between a pair of discharge sustaining electrodes 12. In the plasma display device shown in FIG. 1, a first panel 10, comprising a glass substrate, which corresponds to a front panel and a second panel 20, also comprising a glass substrate, which corresponds to a rear panel are bonded to each other in circumferential portions thereof by using frit glass (not shown) Light emission from fluorescence layers 25 on the second panel 20 is viewed, for example, through the first panel 10.
As shown in FIG. 1, the first panel 10 comprises a transparent first substrate 11; pairs of discharge sustaining electrodes 12, each comprising a transparent electrically conductive material such as ITO, formed on the first substrate 11 in the form of stripes (width being from approximately 80 μm to approximately 280 μm); bus electrodes 13, each comprising a material having a lower electric resistivity than the discharge sustaining electrode 12, formed on the discharge sustaining electrodes 12 for decreasing the impedance of the discharge sustaining electrode 12; a dielectric layer 14 formed on the first substrate 11 as well as on the bus electrodes 13 and discharge sustaining electrodes 12; and a protective film 15, comprising MgO, formed on the dielectric layer 14. A discharge gap G between a pair of the discharge sustaining electrodes 12 is preferably in the range of from 5×10−6 m to 1.5×10−4 m and, particularly preferably, less than 5×10−5 m.
On the other hand, the second panel 20 comprises a second substrate 21; a plurality of address electrodes (also called as data electrodes) 22 formed on the second substrate 21 in the form of stripes; a dielectric material layer 23 formed on the second substrate 21 as well as on the address electrodes 22; insulating separation walls 24, extending in parallel with the address electrodes 22, which are each formed in a region between adjacent address electrodes 22 on the dielectric material layer 23; and fluorescence layers 25 provided on the dielectric material layer 23 and extending to faces of side walls of the separation walls 24. When each of the fluorescence layers 25 performs color display in the plasma display device, the fluorescence layer 25 is constituted by a red fluorescence layer 25R, a green fluorescence layer 25G and a blue fluorescence layer 25B, and the fluorescence layers 25R, 25G and 25B of these colors are provided in a predetermined order. FIG. 1 is a partially exploded perspective view, and in an actual embodiment, top portions of the separation walls 24 on the side of the second panel 20 are in contact with the protective film 15 on the side of the first panel 10. A discharge gas comprising a mixed gas, for example, of neon (Ne) and xenon (Xe) is sealed in each discharge space surrounded by adjacent separation walls 24, the fluorescence layer 25 and the protective film 15.
The extending direction of a projection image of the discharge sustaining electrode 12 and the extending direction of a projection image of the address electrode 22 cross each other at right angles, and a region where a pair of the discharge sustaining electrodes 12 and one combination of the fluorescence layers 25R, 25G and 25B for emitting light in three primary colors overlap corresponds to one pixel. Since glow discharge is caused between a pair of the discharge sustaining electrodes 12, such plasma display device of the above-described type is called as “surface discharge type”. Further, a region where a pair of the discharge sustaining electrodes 12 and the address electrode 22 positioned between two separation walls 24 overlap corresponds to a discharge cell and, also, corresponds to a sub-pixel. That is, one discharge cell (one sub-pixel) is constituted by one fluorescence layer 25, a pair of discharge sustaining electrodes 12 and one address electrode 22.
In driving the plasma display device, for example, a pulse voltage lower than the discharge initiating voltage of the discharge cell is applied to the address electrode 22 immediately before the application of a voltage between a pair of the discharge sustaining electrodes 12. As a result, charges are accumulated in the dielectric layer 14 (selection of a discharge cell for display), and the apparent discharge initiating voltage decreases. Then, the discharge initiated between a pair of the discharge sustaining electrodes 12 can be sustained at a voltage lower than the discharge initiating voltage. In the discharge cell, the fluorescence layer 25 excited by irradiation of a vacuum ultraviolet ray generated by glow discharge in the discharge gas emits light in a color characteristic of a fluorescence material. Further, the vacuum ultraviolet ray having a wavelength according to a kind of the sealed discharge gas is generated.
Such plasma display device as described above starts to appear in the market. However, further reduction of power consumption is required and, to this end, a higher light emission efficiency is required in the plasma display device. Although it is possible to enhance the light emission efficiency by increasing a partial pressure of Xe gas of the discharge gas, when the partial pressure of the Xe gas is increased, a problem is caused in that driving voltage (discharge voltage) is increased or a time delay of discharge is increased.
In the plasma display device having a high partial pressure of Xe, as described above, the dielectric layer 14 is formed on the discharge sustaining electrode 12 in the first substrate 11, and the dielectric layer 14 is ordinarily formed by applying a glass paste, having a low melting point, which comprises, for example, PbO as a major component thereon by using a screen printing method and, then, sintering the thus applied glass paste. Then, the dielectric layer 14 comprising the glass paste having a low melting point comes to be one cause of the increase of the driving voltage or the increase of the time delay of discharge.
In order to decrease the driving voltage, the dielectric layer 14 is allowed to be thin. However, when the dielectric layer 14 comprising the glass paste having a low melting point is allowed to be thin, although the driving voltage is decreased, a problem is caused in that change of luminance along the passage of time becomes large. Further, since the dielectric layer 14 comprising the glass paste having a low melting point has a high specific inductive capacity and a large capacitance, a large amount of current flows, to thereby cause an increase of consumption of current of the plasma display device.
A method for forming the dielectric layer 14 comprising SiOX by using a chemical vapor deposition (CVD) method has been studied. Since the dielectric layer 14 comprising SiOX formed by using the chemical vapor deposition (CVD) method is as low as 4 in the specific inductive capacity and small in the capacitance, an amount of flowing current is small, to thereby realize the decrease of the consumption of current. Further, since SiOX is a dense film, a film thickness of the dielectric layer 14 can be thin, to thereby avoid the increase of the driving voltage. However, in the dielectric layer 14 comprising an ordinary SiOX, the problem of the increase of the time delay of discharge has not been solved.